If I want to try out a different GTK3-Theme using the Unity Shell, I always have troubles with colors of the text. Many themes seem to have trouble with upper bar using similar text colors (i.e. black letters on black unity bar), some themes have great troubles with thunderbird and firefox - in fact even the context menus of thunderbird and firefox in the default ambiance themes are messed up.

Is there a way to manually fix this? I know how to change the colors of the firefox/thunderbird menu texts, but I have no idea about changing the rest.